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MSYNC(2) FreeBSD System Calls Manual MSYNC(2)
NAMEmsync -- synchronize a mapped region
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include <sys/mman.h>
intmsync(void*addr, size_tlen, intflags);
DESCRIPTION
The msync() system call writes any modified pages back to the file system
and updates the file modification time. If len is 0, all modified pages
within the region containing addr will be flushed; if len is non-zero,
only those pages containing addr and len-1 succeeding locations will be
examined. The flags argument may be specified as follows:
MS_ASYNC Return immediately
MS_SYNC Perform synchronous writes
MS_INVALIDATE Invalidate all cached data
RETURN VALUES
The msync() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The msync() system call will fail if:
[EBUSY] Some or all of the pages in the specified region are
locked and MS_INVALIDATE is specified.
[EINVAL] The addr argument is not a multiple of the hardware
page size.
[ENOMEM] The addresses in the range starting at addr and con-
tinuing for len bytes are outside the range allowed
for the address space of a process or specify one or
more pages that are not mapped.
[EINVAL] The flags argument was both MS_ASYNC and MS_INVALI-
DATE. Only one of these flags is allowed.
[EIO] An error occurred while writing at least one of the
pages in the specified region.
SEE ALSOmadvise(2), mincore(2), mlock(2), mprotect(2), munmap(2)HISTORY
The msync() system call first appeared in 4.4BSD.
BUGS
The msync() system call is usually not needed since BSD implements a
coherent file system buffer cache. However, it may be used to associate
dirty VM pages with file system buffers and thus cause them to be flushed
to physical media sooner rather than later.
FreeBSD 11.2 March 18, 2012 FreeBSD 11.2